#include<iostream>
#include<iomanip>
#include<cmath>
using namespace std;

int main()                     //计算两点间的距离    
{
    int xa,xb,ya,yb;
    cin >> xa >> ya ;
    cin >> xb >> yb ;
    double d = sqrt((xa-xb)*(xa-xb)+(ya-yb)*(ya-yb));
    cout << fixed << setprecision(3) << d << endl;
    return 0;
}